Foil specs.
Thickness 16%
Thick point from LE = 20%
LE diameter = 6%
TE = 0.0086956%
Twist = Guesstimate of 3 degrees @ 150N – To be tested with equipment later.
LE sideways deflection = TBA
TE sideways deflection = TBA
Recoil time = TBA
Depth / span = 94.5
Suits fin boxes = FCS

Profile Specs
Area = 86.014 cm2

This is the same fin as Alto except I’ve added tip twist. It looks exactly the same except for a thin slit down the trailing edge. I’ll probably make a test jig sooner or later to test deflection and post some charts with the fins.
The internal structure is very different to the first Alto. Bending it by hand I estimate it’s added 3 degrees to the twist in the top third of the fin. Is this enough? Probably not. It think I want to aim towards 6 or 7 degrees and the flex curve to start earlier towards the base of the board.
I’ll estimate that on sideways take offs that you’ll get planing marginally earlier than alto and through the turns you’ll be able to press harder which will actually increase speed. The flex and recoil will give more drive through a bottom turn. It should allow you to feel the fin loading through the turn and govern when you lose traction.

Note The split on the trailing edge allows twist, but the 3D print head may melt the surfaces together a little bit. Run a blade down the split to crack it apart.

Feedback from first tests.

The fin appears to be handling as expected. It is definitely much faster than Alto and is much more controllable through the turn. The is about a 20% loss in initial take off lift due to the tip twist, but an increase in control and power through the turn. A slightly larger fin will compensate for the lost lift. Maybe say 20% more surface area.